CM Current MeasurementFollow
Current measurement (CM) is a facility available on all Radiodetection Precision Locators. The current information can help to sort out difficult locates in congested situations and improve identification.
Current measurement can only be accurate when a locator is detecting a ‘clean’ signal from a single conductor and is very dependent on depth accuracy. For this reason, CM is only available in the Active modes, not for passive signals, and should only be used when a site has been checked for distorted signals as for depth measurement.
What Is Current Measurement?
Exactly what it sounds like. Most locators only give an output of signal strength which may be dependent on the actual gain setting of the receiver at a particular time and is usually dependent on depth. If the signal strength display is dependent on depth, the displayed quantity decreases as the depth increases. This can lead to errors when tracing signals from several targets at different depths. The errors result from assuming that the line which gives the strongest response is the line carrying the strongest signal. In many cases the deeper line is carrying the strongest signal but does not show the strongest response, as illustrated below.
How does CM work?
CM is an extension of the principles used for depth measurement. The diagram shows the signals detected by the two search coils and the computation that is performed to derive current.
The constant k is proportional to sensitivity and is chosen so that kI is a direct read out in mA.